1. Field of the Invention
The present invention relates to a scanning probe microscope comprising a cantilever having in its tip a probe, and observing a sample, and an electric potential difference detection method detecting an electric potential difference occurring between a surface of the sample and the probe of the cantilever.
2. Description of the Related Art
As a device for performing an observation of a physical property information, such as surface shape or viscoelasticity, of the sample, and the like by measuring in a micro region of the sample of metal, semiconductor, ceramic, resin, high polymer, biomaterial, insulator and the like, there is known the scanning probe microscope (SPM: Scanning Probe Microscope). As the scanning probe microscope, there is an AFM (Atomic Force Mode), a DFM (Dynamic Force Mode) or the like. The AFM is one in which the probe formed in a tip part of a cantilever supported like a cantilever beam of a mounted probe is scanned on a surface of the sample, and a displacement quantity of the displaced probe is measured by the surface shape of the sample, thereby measuring the surface shape of the sample. Further, the DFM is one in which the above-mentioned cantilever is resonated and, by its amplitude change, phase change or frequency change, the surface shape of the sample is measured (e.g., refer to Patent Document 1: JP-A-2003-42931 Gazette).
Further, besides the scanning probe microscope like the above, as special ones, there are a Kelvin probe force microscope (e.g., refer to Patent Document 2: JP-A-2004-226237 Gazette), a scanning Maxwell stress microscope (e.g., refer to Patent Document 3: JP-A-2002-55040 Gazette), and the like. These comprises a lock-in amplifier capable of synchronously detecting a predetermined frequency component, and an electric potential measuring control circuit having an adder, an integrator and the like, and it is possible to analyze a surface electric potential image of the sample respectively by, in the former, finding such an amplitude output as to minimize a static electricity force between the probe and the sample and by, in the latter, finding such a DC voltage as to make an amplitude of the predetermined frequency component zero.
However, in the scanning probe microscope like the Patent Document 1, in such a case that the sample is electrified, the electric potential difference occurs between the surface of the sample and the probe of the cantilever, and it follows that the static electricity force by this electric field acts on the cantilever. Therefor, in the case like this, there is an issue that the electric potential difference exerts an influence on a displacement of the cantilever at a sample observation time and thus a measurement becomes impossible, or it becomes impossible to obtain an accurate observation image. In the case like this, although it is necessary to perform such an action as to dissolve the electric potential difference, there is a case where it is difficult to judge from an observation image obtained whether the observation image is accurate one or one undergoing the influence of the electric potential difference.
On the other hand, in the Kelvin probe force microscope of the Patent Document 2 and the scanning Maxwell stress microscope of the Patent Document 3, by comprising the lock-in amplifier and the electric potential measuring control circuit, it is possible to detect the electric potential difference like the above, and it is possible to dissolve the above issue. However, the constitution like this is not mounted in the scanning probe microscope like the Patent Document 1, in which the measurement is performed by the AFM, the DFM and the like. Therefor, in order to detect the electric potential difference by a method of the Patent Document 2 or the Patent Document 3, although it is necessary to mount the lock-in amplifier and the electric potential measuring control circuit, a device cost increases and, further suppositively even if they are mounted, it is necessary to perform a complicated measurement method, so that there is an issue that it takes a time.